An integrated circuit (IC) package is a housing which environmentally protects the IC, facilitates testing of the IC, and facilitates the use of the IC in high-yield assembly processes. Such a package functions to protect an IC from mechanical and environmental stresses and electrostatic discharge. It also functions to provide a mechanical interface for testing, burn-in, and interconnection to a higher level of packaging such as a circuit card.
In many IC packages a substrate acts as an interconnecting layer between the terminals or pads on the IC, and the connectors or leads of the package. The substrate is typically mechanically and electrically coupled to both the IC and the package leads. The substrate may be made from a ceramic or organic material, may be rigid or flexible, and may comprise a single layer or multiple layers laminated together.
A substrate typically has two substantially planar sides located on opposite sides of the substrate. A substrate may include conductive patterns located on one or both of the planar sides, and may include conductive through holes or vias to provide a conductive path through the substrate. Substrate fabrication may include the steps of providing a base layer such as a polyimide film, forming vias in the base layer, covering the planar surfaces of the base layer with one or more metal layers and filling the vias with conductive material, removing portions of the metal layers to form the conductive pattern, and possibly coupling the resulting substrate with additional substrates to form a multi-layer substrate.
The step of forming vias in the base layer may be accomplished through the use of laser drilling. Although laser drilling provides many benefits, it typically leaves surface contaminants ("laser slag") on the substrate surfaces. These surface contaminants are preferably removed prior to covering the surfaces with the metal layers. Although chemical and plasma cleaning methods are known, improvements in substrate cleaning have the potential of providing substantial economical and environmental savings.
The step of covering the surfaces of the base layer with one or more metal layers and filling the vias with conductive material is preferred to result in sufficient adhesion of the metal layers to the base layer so as to prevent future delamination. A measure of the ability to resist delamination is peel strength. Peel strength is typically measured as units of force per unit width such as lb/in or g/mm and is determined by measuring the amount of force required to peel a strip of the metal layer from the base layer.
Existing methods and devices sometimes produce an unsatisfactory result in that the resulting coated substrate suffer from relatively poor peel strength on one or more sides. Thus, it is desirable to develop new substrates having higher peel strengths, and methods and devices for producing such substrates.